The invention relates to a method for producing aminoorganosilanes by reacting amines with (haloorganyl)silanes and liberating the by-produced ammonium halide of the amine with a base.
The prior art discloses various methods for producing aminoorganosilanes. The production of amino functional organosilanes is effected predominantly by reacting chlorofunctional organosilanes with very different types of organic amines or ammonia. As a rule, the procedure is such that at least two moles of amine or ammonia are used per mole of chlorofunctional organosilane, so that, in addition to the formation of the aminofunctional organosilane, there is still sufficient amine component available for converting the substituted chlorine into the corresponding amine hydrochloride or ammonium chloride.
In particular, the high availability of (chloroalkyl)-silanes, which are obtainable by means of photochlorination of alkylsilanes or hydrosilylation of corresponding halogen-substituted olefins on Si—H-containing compounds and are used, for example, as intermediates for the synthesis of a multiplicity of organofunctional silanes, is advantageous here.
Furthermore, it is possible in this method to rely not only on ammonia but also on a large number of readily available primary and secondary amines for synthesizing the (N-organylaminoorganyl)- and (N,N-diorganylamino-organyl)triorganylsilanes, which permits a very wide area of use of the method and thereby economical product change on existing industrial manufacturing plants.
GB 686,068 A discloses (amino)-, (N-organylamino)- and (N,N-diorganylaminomethyl)- or (N,N-diorganylamino-ethyl)triorganylsilanes. Furthermore, GB 686,068 A describes a method for reacting corresponding (chloromethyl)- or (bromomethyl)triorganosilanes with ammonia, a primary or secondary amine at temperatures of at least 50° C. for the production of said (aminoorganyl)-, (N-organylaminoorganyl)- and (N,N-diorganylaminoorganyl)triorganylsilanes. As a rule, the (chloromethyl)- or (bromomethyl)triorganosilanes are initially introduced into a flask or autoclave, depending on the boiling points of the amine compounds used, and are heated to temperatures above 100° C., preferably 110-130° C. In the case of higher-boiling amines (e.g. cyclohexylamine), the sequence of mixing can be reversed, i.e. the (chloromethyl)- or (bromomethyl)triorganosilanes are added to the heated amine.
According to a method described in DE 1812564 A1, (aminomethyl)silane derivatives are produced by reacting a (chloromethyl)- or (bromomethyl)silane derivative with ammonia or a primary amine. The reaction is effected at temperatures of 80 or 100° C. in a period of 3 or 2 hours, the amine having been completely initially introduced in a molar excess of 1:3.2-6 as early as the beginning of the reaction.
DE 10 2004 060 627 A describes a variation of these methods in which the abovementioned reactions are carried out continuously.
The prior art further discloses methods for reducing halide contents in alkoxysilanes, for example EP 0702017 A discloses those which are based on the precipitation of dissolved amine hydrochloride moieties by addition of alkali metal or alkaline earth metal alcoholate salts. An alternative method which is said to permit reductions of chloride contents in alkoxysilanes by introduction of ammonia is described in DE 19941283 A1.
A disadvantage of all these methods is the fact that (optionally organically substituted) ammonium halides are formed in quantitative amounts as byproducts and have to be separated off as solids. Separating off such large amounts of solid is time-consuming and hence expensive and moreover requires production plants which have appropriate apparatuses, for example powerful and therefore expensive centrifuges. However, this is not the case in many plants—in particular in most multipurpose plants as are typically used for producing fine chemicals.
Here, for example, U.S. Pat. No. 6,452,033 A describes the production of aminoethylaminoorganyltriorganylsilanes by reacting the corresponding chlorofunctional organosilanes with ethylenediamine, the above-mentioned phase separation for separating the hydrochlorides being used in various ways. However, a disadvantage of this method is the fact that it is limited to silanes which have an ethylenediamine unit.
DE 102007037193 A describes a process for production of aminoorganyltriorganylsilanes which comprises a first step of reacting a halo(organyl)silane with an amine to form an amino-functional silane (and by-produce the amine hydrohalide) and a second step of using a base to liberate the amine again from the hydrohalide formed, wherein the base's hydrohalide formed in this double decomposition is liquid at up to 200° C. and therefore this salt phase can be separated off via simple liquid/liquid phase separation. In the process, a phase equilibrium becomes inevitably established depending on the solubilities of the components involved, and determines the composition of the two phases. To isolate the target product and achieve quantitative recovery of the amine, therefore, it is essential that these two components shall ideally not accumulate in the salt phase of the hydrohalide of the base, since this hydrohalide is typically disposed of or recycled. Particularly in the case of polar amines, however, accumulation in the salt phase is frequently observed, and so the salt phase has to be worked up at some cost and inconvenience to quantitatively recover the amines. For example, when primary amines are reacted with haloalkylsilanes to form the corresponding monosubstitution products, a substantially loss-free recovery of amine requires distillative removal of excess amine even before adding the base.
The object was to develop a method which no longer has the disadvantages of the prior art.